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25 pages, 41078 KiB

Open AccessArticle

Comparative Drought Responses of Quercus ilex L. and Pinus sylvestris L. in a Montane Forest Undergoing a Vegetation Shift

by David Aguadé, Rafael Poyatos, Teresa Rosas and Jordi Martínez-Vilalta

Forests 2015, 6(8), 2505-2529; https://doi.org/10.3390/f6082505 - 27 Jul 2015

Cited by 56 | Viewed by 7766

Abstract

Different functional and structural strategies to cope with water shortage exist both within and across plant communities. The current trend towards increasing drought in many regions could drive some species to their physiological limits of drought tolerance, potentially leading to mortality episodes and [...] Read more.

Different functional and structural strategies to cope with water shortage exist both within and across plant communities. The current trend towards increasing drought in many regions could drive some species to their physiological limits of drought tolerance, potentially leading to mortality episodes and vegetation shifts. In this paper, we study the drought responses of Quercus ilex and Pinus sylvestris in a montane Mediterranean forest where the former species is replacing the latter in association with recent episodes of drought-induced mortality. Our aim was to compare the physiological responses to variations in soil water content (SWC) and vapor pressure deficit (VPD) of the two species when living together in a mixed stand or separately in pure stands, where the canopies of both species are completely exposed to high radiation and VPD. P. sylvestris showed typical isohydric behavior, with greater losses of stomatal conductance with declining SWC and greater reductions of stored non-structural carbohydrates during drought, consistent with carbon starvation being an important factor in the mortality of this species. On the other hand, Q. ilex trees showed a more anisohydric behavior, experiencing more negative water potentials and higher levels of xylem embolism under extreme drought, presumably putting them at higher risk of hydraulic failure. In addition, our results show relatively small changes in the physiological responses of Q. ilex in mixed vs. pure stands, suggesting that the current replacement of P. sylvestris by Q. ilex will continue. Full article

(This article belongs to the Special Issue Responses of Forest Trees to Drought)

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11 pages, 413 KiB

Open AccessArticle

Variation of Oriental Oak (Quercus variabilis) Leaf δ¹³C across Temperate and Subtropical China: Spatial Patterns and Sensitivity to Precipitation

by Baoming Du, Hongzhang Kang, Yanhua Zhu, Xuan Zhou, Shan Yin, Paul J. Burgess and Chunjiang Liu

Forests 2015, 6(7), 2296-2306; https://doi.org/10.3390/f6072296 - 30 Jun 2015

Cited by 13 | Viewed by 6451

Abstract

The concentration of the carbon-13 isotope (leaf δ¹³C) in leaves is negatively correlated with the mean annual precipitation (MAP) atlarge geographical scales. In this paper, we explain the spatial pattern of leaf δ¹³C variation for deciduous oriental oak ( [...] Read more.

The concentration of the carbon-13 isotope (leaf δ¹³C) in leaves is negatively correlated with the mean annual precipitation (MAP) atlarge geographical scales. In this paper, we explain the spatial pattern of leaf δ¹³C variation for deciduous oriental oak (Quercus variabilis Bl.) across temperate and subtropical biomes and its sensitivity to climate factors such as MAP. There was a 6‰ variation in the leaf δ¹³C values of oak with a significant positive correlation with latitude and negative correlations with the mean annual temperature (MAT) and MAP. There was no correlation between leaf δ¹³C and altitude or longitude. Stepwise multiple regression analyses showed that leaf δ¹³C decreased 0.3‰ per 100 mm increase in MAP. MAP alone could account for 68% of the observed variation in leaf δ¹³C. These results can be used to improve predictions for plant responses to climate change and particularly lower rainfall. Full article

(This article belongs to the Special Issue Responses of Forest Trees to Drought)

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15 pages, 32461 KiB

Open AccessArticle

Adaptation of Leaf Water Relations to Climatic and Habitat Water Availability

by Patrick J. Mitchell and Anthony P. O'Grady

Forests 2015, 6(7), 2281-2295; https://doi.org/10.3390/f6072281 - 30 Jun 2015

Cited by 23 | Viewed by 6082

Abstract

Successful management of forest systems requires a deeper understanding of the role of ecophysiological traits in enabling adaptation to high temperature and water deficit under current and anticipated changes in climate. A key attribute of leaf water relations is the water potential at [...] Read more.

Successful management of forest systems requires a deeper understanding of the role of ecophysiological traits in enabling adaptation to high temperature and water deficit under current and anticipated changes in climate. A key attribute of leaf water relations is the water potential at zero turgor (π_tlp), because it defines the operating water potentials over which plants actively control growth and gas exchange. This study examines the drivers of variation in π_tlp with respect to species climate of origin and habitat water availability. We compiled a water relations database for 174 woody species occupying clearly delineated gradients in temperature and precipitation across the Australian continent. A significant proportion of the variability in π_tlp (~35%) could be explained by climatic water deficit and its interaction with summertime maximum temperature, demonstrating the strong selective pressure of aridity and high temperature in shaping leaf water relations among Australian species. Habitat water availability (midday leaf water potential), was also a significant predictor of π_tlp (R² = 0.43), highlighting the importance of species ecohydrologic niche under a set of climatic conditions. Shifts in π_tlp in response to both climatic and site-based drivers of water availability emphasises its adaptive significance and its suitability as a predictor of plant performance under future climatic change. Full article

(This article belongs to the Special Issue Responses of Forest Trees to Drought)

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20 pages, 1461 KiB

Open AccessArticle

Regulation of Water Use in the Southernmost European Fir (Abies pinsapo Boiss.): Drought Avoidance Matters

by Raúl Sánchez-Salguero, Cristina Ortíz, Felisa Covelo, Victoria Ochoa, Roberto García-Ruíz, José Ignacio Seco, José Antonio Carreira, José Ángel Merino and Juan Carlos Linares

Forests 2015, 6(6), 2241-2260; https://doi.org/10.3390/f6062241 - 19 Jun 2015

Cited by 20 | Viewed by 7354

Abstract

The current scenario of global warming has resulted in considerable uncertainty regarding the capacity of forest trees to adapt to increasing drought. Detailed ecophysiological knowledge would provide a basis to forecast expected species dynamics in response to climate change. Here, we compare the [...] Read more.

The current scenario of global warming has resulted in considerable uncertainty regarding the capacity of forest trees to adapt to increasing drought. Detailed ecophysiological knowledge would provide a basis to forecast expected species dynamics in response to climate change. Here, we compare the water balance (stomatal conductance, xylem water potential, needle osmotic adjustment) of Abies pinsapo, a relict drought-sensitive Mediterranean fir, along an altitudinal gradient. We related these variables to soil water and nutrient availability, air temperature, atmospheric water potential, and vapour pressure deficit during two consecutive years. Our results indicate that A. pinsapo closed stomata rapidly over a very narrow range of soil water availability and atmospheric dryness. This isohydric response during water stress suggests that this relict conifer relied on the plant hormone abscisic acid to maintain closed stomata during sustained drought, instead of needle desiccation to passively drive stomatal closure, needle osmotic adjustment or a plastic response of the xylem to different levels of water availability. Both the soil and foliar nutrient contents suggest that the studied populations are not limited by nutrient deficiencies, and drought was stronger in the warmer low-elevation areas. Full article

(This article belongs to the Special Issue Responses of Forest Trees to Drought)

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23 pages, 7117 KiB

Open AccessArticle

Modeling of Two Different Water Uptake Approaches for Mono- and Mixed-Species Forest Stands

by Martin Gutsch, Petra Lasch-Born, Felicitas Suckow and Christopher P.O. Reyer

Forests 2015, 6(6), 2125-2147; https://doi.org/10.3390/f6062125 - 12 Jun 2015

Cited by 7 | Viewed by 6379

Abstract

To assess how the effects of drought could be better captured in process-based models, this study simulated and contrasted two water uptake approaches in Scots pine and Scots pine-Sessile oak stands. The first approach consisted of an empirical function for root water uptake [...] Read more.

To assess how the effects of drought could be better captured in process-based models, this study simulated and contrasted two water uptake approaches in Scots pine and Scots pine-Sessile oak stands. The first approach consisted of an empirical function for root water uptake (WU1). The second approach was based on differences of soil water potential along a soil-plant-atmosphere continuum (WU2) with total root resistance varying at low, medium and high total root resistance levels. Three data sets on different time scales relevant for tree growth were used for model evaluation: Two short-term datasets on daily transpiration and soil water content as well as a long-term dataset on annual tree ring increments. Except WU2 with high total root resistance, all transpiration outputs exceeded observed values. The strongest correlation between simulated and observed annual tree ring width occurred with WU2 and high total root resistance. The findings highlighted the importance of severe drought as a main reason for small diameter increment. However, if all three data sets were taken into account, no approach was superior to the other. We conclude that accurate projections of future forest productivity depend largely on the realistic representation of root water uptake in forest model simulations. Full article

(This article belongs to the Special Issue Responses of Forest Trees to Drought)

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10 pages, 3616 KiB

Open AccessCommunication

Early Differential Responses of Co-dominant Canopy Species to Sudden and Severe Drought in a Mediterranean-climate Type Forest

by Katinka X. Ruthrof, George Matusick and Giles E. St. J. Hardy

Forests 2015, 6(6), 2082-2091; https://doi.org/10.3390/f6062082 - 9 Jun 2015

Cited by 32 | Viewed by 6546

Abstract

Globally, drought and heat-induced forest disturbance is garnering increasing concern. Species from Mediterranean forests have resistance and resilience mechanisms to cope with drought and differences in these ecological strategies will profoundly influence vegetation composition in response to drought. Our aim was to contrast [...] Read more.

Globally, drought and heat-induced forest disturbance is garnering increasing concern. Species from Mediterranean forests have resistance and resilience mechanisms to cope with drought and differences in these ecological strategies will profoundly influence vegetation composition in response to drought. Our aim was to contrast the early response of two co-occurring forest species, Eucalyptus marginata and Corymbia calophylla, in the Northern Jarrah Forest of southwestern Australia, following a sudden and severe drought event. Forest plots were monitored for health and response, three and 16 months following the drought. Eucalyptus marginata was more susceptible to partial and complete crown dieback compared to C. calophylla, three months after the drought. However, resprouting among trees exhibiting complete crown dieback was similar between species. Overall, E. marginata trees were more likely to die from the impacts of drought, assessed at 16 months. These short-term differential responses to drought may lead to compositional shifts with increases in frequency of drought events in the future. Full article

(This article belongs to the Special Issue Responses of Forest Trees to Drought)

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19 pages, 5659 KiB

Open AccessArticle

How do Light and Water Acquisition Strategies Affect Species Selection during Secondary Succession in Moist Tropical Forests?

by Leonie Schönbeck, Madelon Lohbeck, Frans Bongers, Miguel Martínez Ramos and Frank Sterck

Forests 2015, 6(6), 2047-2065; https://doi.org/10.3390/f6062047 - 8 Jun 2015

Cited by 21 | Viewed by 7225

Abstract

Pioneer tree species have acquisitive leaf characteristics associated with high demand of light and water, and are expected to be shade and drought intolerant. Using leaf functional traits (specific leaf area, photosynthetic rate, relative water content and stomatal conductance) and tree performance (mortality [...] Read more.

Pioneer tree species have acquisitive leaf characteristics associated with high demand of light and water, and are expected to be shade and drought intolerant. Using leaf functional traits (specific leaf area, photosynthetic rate, relative water content and stomatal conductance) and tree performance (mortality rate) in the field, we assessed how shade and drought tolerance of leaves are related to the species’ positions along a successional gradient in moist tropical forest in Chiapas, Mexico. We quantified morphological and physiological leaf shade and drought tolerance indicators for 25 dominant species that characterize different successional stages. We found that light demand decreases with succession, confirming the importance of light availability for species filtering during early stages of succession. In addition, water transport levels in the leaves decreased with succession, but high water transport did not increase the leaf’s vulnerability to drought. In fact, late successional species showed higher mortality in dry years than early successional ones, against suggestions from leaf drought tolerance traits. It is likely that pioneer species have other drought-avoiding strategies, like deep rooting systems and water storage in roots and stems. More research on belowground plant physiology is needed to understand how plants adapt to changing environments, which is crucial to anticipate the effects of climate change on secondary forests. Full article

(This article belongs to the Special Issue Responses of Forest Trees to Drought)

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22 pages, 43453 KiB

Open AccessArticle

Timing of Drought Triggers Distinct Growth Responses in Holm Oak: Implications to Predict Warming-Induced Forest Defoliation and Growth Decline

by J. Julio Camarero, Magí Franquesa and Gabriel Sangüesa-Barreda

Forests 2015, 6(5), 1576-1597; https://doi.org/10.3390/f6051576 - 5 May 2015

Cited by 72 | Viewed by 8334

Abstract

Droughts negatively impact forests by reducing growth and increasing defoliation leading to forest dieback as the climate becomes warmer and drier. However, the timing and severity of droughts determine how differently or intensively water shortage affects primary (shoot and leaf formation) and secondary [...] Read more.

Droughts negatively impact forests by reducing growth and increasing defoliation leading to forest dieback as the climate becomes warmer and drier. However, the timing and severity of droughts determine how differently or intensively water shortage affects primary (shoot and leaf formation) and secondary growth (stem radial growth based on tree-ring widths). We compare the impact of two severe droughts (2005, 2012), showing different climatic characteristics on the growth responses of three Mediterranean holm oak stands in northeastern Spain. We also quantify climate trends and drought severity. Then, we use remote sensing data to infer how those droughts impacted forest productivity. Both droughts were characterized by warm and dry spring conditions leading to reduced budburst, low shoot production, asynchrony in primary growth and decreased productivity and scarce radial growth, particularly in 2005. However, defoliation peaked in 2012 when radial growth showed minimum values and early spring and late summer temperatures reached maximum values. We discuss how uncoupled and resilient are the responses of primary and secondary growth to drought. Finally, these findings are used to gain insight into the drought-related drivers of defoliation in Spanish holm oak forests. Full article

(This article belongs to the Special Issue Responses of Forest Trees to Drought)

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Review

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18 pages, 9258 KiB

Open AccessReview

Are Mixed Tropical Tree Plantations More Resistant to Drought than Monocultures?

by Norbert Kunert and Alida Mercado Cárdenas

Forests 2015, 6(6), 2029-2046; https://doi.org/10.3390/f6062029 - 5 Jun 2015

Cited by 34 | Viewed by 10933

Abstract

Tropical tree plantations usually consist of a single exotic fast growing species, but recent research describes positive effects on ecosystem functions from mixed tropical tree plantations. In this review, we present the current knowledge of drought resistance of tropical mixed species plantations and [...] Read more.

Tropical tree plantations usually consist of a single exotic fast growing species, but recent research describes positive effects on ecosystem functions from mixed tropical tree plantations. In this review, we present the current knowledge of drought resistance of tropical mixed species plantations and summarize preliminary evidence from a tree biodiversity experiment in Panama. Converting mono-specific stands into mixed ones may improve stand stability and might reduce increasing abiotic and biotic disturbances due to climate change. However, little is known about the extent to which tropical tree species or tropical tree communities can resist increasing disturbances in the short term, e.g., water limitations due to increasing dry season intensity or length, or about their resilience after such disturbances and their capacity to adapt to changing conditions in the long term. Studies relating drought resistance and resilience to community diversity are missing. Further, we highlight the urgent need for a multifactorial manipulative throughfall reduction experiment in tropical environments. The outcome of such studies would greatly assist the forestry sector in tropical regions to maintain highly productive and ecologically sound forest plantations in a changing climate. Full article

(This article belongs to the Special Issue Responses of Forest Trees to Drought)

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